assigner init should be able to copy values from another config

[LinuxMercedes]

Give init an optional argument; if it's a path to a directory, we try to load a config from the _config.yml in that directory; if it's a file, we try to load it as a config.

From this config, init should be able to copy these config settings:

• backend config
• canvas host
• canvas token

Anything else set by init will still need to be prompted for.